The Left 4 Dead Blog has some juicy bits about Steam Workshop coming to Left 4 Dead as Linux.
All of this will also be available not just on the PC and Mac, but also for Linux users as well starting in the middle of next month and rolling out from there. We will have more details as we get closer to launch.
I’m honestly not a L4D player, so I wholly admit that I could be reading this wrong (though where I saw it posted said “Steam coming to linux confirmed”), as I don’t really know what the Steam Workshop is or how that relates, but anything that’s Steam related that is coming to Linux is a good thing, and does follow previous rumors about Valve working on a Linux port.